A novel protection relay for neutral effectively grounded distribution networks independent on sequence components

Abstract

The neutral effectively grounded system (NEGS), increasingly adopted in medium-voltage urban AC distribution networks, exhibits heightened susceptibility to fault-induced overcurrent. Despite the deployment of traditional three-zone and zero-sequence overcurrent protection relays, they continue to struggle with sensitivity and speed limitations. A further complication arises from the prevailing reliance on the zero-sequence component, given the practical difficulties associated with installing zero-sequence current transformers (CTs). To overcome these challenges, this paper introduces a protection relay that works independently of the sequence component, offering superior speed, sensitivity, and robustness. First, it is established that any given phase’s superimposed faulted phase current (SFPC) bears a consistent distribution pattern, irrespective of the fault type. This distinctive attribute is represented by introducing the concept of the postfault locus (PFL). Then, a novel protection relay is proposed, which computes the PFL based on the inner product of individual feeders and a reference phasor. Furthermore, integrating the phaselet algorithm augments the relay’s response speed while effectively mitigating the risk of CT saturation. Case studies demonstrate that the proposed relay boasts sufficient sensitivity, tolerating fault resistance up to 2000 O, and has sufficient robustness under noise contamination of 30 dB.